1. Field
Exemplary embodiments of the present invention relate to a semiconductor design technology, and more particularly, to a counting circuit, an image sensing device with the counting circuit and a read-out method of the image sensing device.
2. Description of the Related Art
Image sensing devices capture images using the photosensitive properties of semiconductors. Image sensing devices may be classified into charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors. The CMOS image sensors have come into widespread use. This is because CMOS image sensors allow analog circuits and digital control circuits to be realized on a single integrated circuit (IC).
The image sensing device employs high dynamic range (HDR) technology to provide a clear image. The HDR technology generally adopts a frame multiple capture method. According to the frame multiple capture method, images are synthesized by capturing successive frames at different exposure times. However, the frame multiple capture method requires a frame memory, and thus it is difficult to use the frame multiple capture method in the mobile field using limited resources. Thus, there has been proposed HDR technology which reflects different exposure times on a 2-row basis. In the HDR technology, however, motion artifact may occur when images are synthesized. In order to improve such a problem, the solid-state imaging device and camera system of U.S. Pat. No. 8,643,755 (“Nishihara”) has been proposed. Nishihara uses different analog gains for the same pixel and thus obtains results into which different exposure times are reflected. The device of Nishihara performs a read-out operation through Correlated Double Sampling (CDS) during first analog to digital (A/D) conversion for a small ramping slope, and performs a read-out operation through delta-reset sampling (DRS) during second A/D conversion for a great ramping slope. Nishihara can remove KT/C noise through CDS during the first A/D conversion, but cannot remove KT/C noise through DRS during the second A/D conversion.
Since the KT/C noise relies on the switch-off characteristic of a transistor, to which a reset signal RX is inputted, among transistors included in the pixel, the KT/C noise randomly occurs whenever the transistor is switched off.
Furthermore, Nishihara may generate only two image data corresponding to two analog gains. In other words, Nishihara cannot generate three or more image data corresponding to three or more analog gains.